I saw some post on Cuba here.
You can legally stay at a registered casa particular.
You only have to put the addres (and if possible registration number) on your tourist card.
If you are looking for a casa in Cuba: visit www.casaparticular.info
This non-commercial (no reservation service) mini portal has links to over 300 websites that offer one or more "casas" in Cuba. The Havana page itself has 157 links to sites.
You will also find info on buses, trains, car rental, pharmavies, internet access, restaurants and paladares, cycling, diving, climbing, maps, guides, books, ...
I have done the legwork. Enjoy it.

This apartment is situated close to the center of Cienfuegos and near to the bus/ train station in a interesting & safe neighborhood .It has two double rooms(air conditioner ,fan ,comfortable beds ,etc) with bathrooms with cold & warm water all day .The living-room is great with a TV ,video ,dvd , cd player(with a lot of Cuban music),video games ,etc .In the kitchen you have a gas- cooker ,two refrigerator ,a microwave ,an electric rice cooker ,etc. There is also a dinner table with six chairs .In the terrace you have a nice view of the city and you also have a washing machine to wash your clothes.

The owners are a young English spoken couple, and they will help you in everything you need for sure .He is a tourist guide and she is studying at the university her last year of sport training(she is a professional massager and a very good cook).
You can ask them for:
--Good breakfast ,lunch ,dinner(specially sea food or chicken and pineapple mixed),
--A taxi driver(English spoken) to bring you everywhere,(beaches ,dolphins show or bath ,crocodiles place ,Ché Guevara or Bay of Pigs museums ,waterfalls ,others cities ,etc,
--To wash your clothes,
--Rent bikes,
--An old American car to drive around the city,
--Where to get rum ,cigars ,coffee ,souvenirs ,etc,
--and more….

Any questions or help you need ,please ,email me